Residual testing solutions

Comprehensive sterilization processing and associated laboratory test service to the healthcare manufacturing industry

Any medical device, sterilized by Ethylene Oxide that is patient contacting, must undergo residual testing to analyze the EO residual levels. The residues can be harmful to the end user or patient so it is important that all devices meet the limits set forth in the ISO 10993-7 standard.

The limits will vary depending upon the intended use of the device as there are three main categories a device may fall under: limited use, prolonged use and permanent use. In addition, there are several special device categories that have their own unique set of limits. Devices that do not have patient contact are not required to meet this standard.

Devices considered as surface contacting or implantable must meet an additional set of criteria called the tolerable contact limit (TCL). The purpose of this limit is to prevent localised irritation due to the release of EO or ECH from the device. The TCL is a calculated value that takes into consideration the surface area of a device and the EO and ECH residue levels in order to determine if irritation will be an issue.

Root causes to high residual levels?

There are several reasons why a device may contain high levels of residues after being exposed to the ethylene oxide sterilization process:
Material – certain materials will absorb and retain gas molecules more than others. Natural materials such as cellulose and cotton are known to be very absorbent. Some types of plastics have also known to show high absorption rate when exposed to EO processing.

Packaging – EO processing requires breathable packaging such as Tyvek or medical grade paper to allow the gas molecule to pass through. Packaging with a minimal or obstructed breathable surface area (i.e., large adhesive label) will not allow gas to move as freely across the breathable barrier.

Load configuration – the volume, density and overall configuration of the load on a pallet can impact the ability of gas removal after processing.

Ways to reduce residual levels?

The good news is that most residue can be overcome with a few simple changes to the existing sterilization parameters if an eo process is currently in place. For new devices manufacturers, residue issues can likely be eliminated up front by considering the following methods while developing the sterilization parameters.

Nitrogen washes – all cycles will have a nitrogen wash phase after the EO gas has been evacuated from the sterilization chamber. Adding nitrogen aids in diluting the EO in the headspace of the chamber, thus reducing the residues left behind. Increasing the number of washes as well as performing them at a deeper vacuum can be beneficial.

Added heat – heat aids in the off gassing process so it is helpful to keep as much heat in the chamber as possible after the sterilization process. This can be done a few ways such as increasing the overall processing temperature set point or adding a moisture conditioning phase after the EO has been removed.

Extended aeration – after the in-chamber process has been completed the load may be transferred into a heated aeration cell to aid in further off-gassing. The industry average for a typical aeration time is 6 to 24 hours. Some devices may require no heated aeration and others may require a period beyond the industry average. Extending the duration that a load is in heated aeration can be beneficial if necessary.

Why use STERIS Pharmaceutical Laboratories for residual testing?

STERIS Pharmaceutical Laboratories provides a comprehensive sterilization processing and associated laboratory test service to the healthcare manufacturing industry – A huge bonus when it comes to residual testing.

We can offer the benefits of twenty years experience as a contract EO sterilization residual testing laboratory. We also offer the added bonus that our laboratory operates directly with the process team to work with Customers and their sterilization requirements.

A key factor for residual testing is the retrieval of samples and storage below -10°C. In Tullamore, there is no need for transporting samples on dry ice from one plant to another. Samples are removed from a load and placed in a freezer, only walking distance away, at temperatures <-10°C

There are many years of technical expertise available in our contract laboratory.

The high sample throughput allows testing of the samples to be carried out within days of removal to the warehouse freezers. Depending on the extraction method, results can be available within 2 days of testing, and the team work closely with customers providing continuous updates on the progression of testing.

In the event of questions or problems with residual testing, our experienced and competent technical experts are available to act as contact person to the Customer.

Contact our team of experts to find out more about our Residual Testing Services